(a) Technical Field
The present invention relates to a technique for controlling transitioning between an electric vehicle (EV) mode and a hybrid electric vehicle (HEV) mode in a hybrid vehicle. More particularly, it relates to a technique for controlling transitioning between an EV mode and an HEV mode in a hybrid vehicle, which determines a drive mode of the hybrid vehicle and determines an engine on map value and a hysteresis map value, which are related to the transition between the EV mode and the HEV mode, differently for each drive mode.
(b) Background Art
A hybrid vehicle is a vehicle that is powered two or more power sources. On well known hybrid vehicle is a gas/electric hybrid vehicle which is powered by both a gasoline engine and an electric motor. When the hybrid vehicle is driven by the gasoline engine in an inefficient driving environment, the efficiency of the overall system can be improved by charging or discharging the electric motor (load leveling). Moreover, during deceleration driving, frictional heat generated during a braking operation is converted into kinetic energy and emitted to the air. Here, it is possible to generate electricity (i.e., through a regenerative braking process) using the kinetic energy supplied by the braking action to rotate the electric motor in reverse and store the resulting electricity in a battery, thereby improving the fuel efficiency of the hybrid vehicle.
However, in a hybrid vehicle, the on/off control of the gasoline engine and the control of power distribution between the engine and the motor have a significant effect on the fuel efficiency and driving performance of the hybrid vehicle overall. Moreover, the on/off control of the engine and the control of power distribution between the engine and the motor are associated with various factors such as, for example, the vehicle's speed which his measured by a vehicle speed sensor, a value measured by an accelerator position sensor (APS), a value measured by a gear position sensor, a battery's state-of-charge (SOC), etc., and thus the on/off control of the engine and the control of power distribution between the engine and the motor are performed based on the combination of these factors.
In particular, it is often important to appropriately determine a specific time for transition between the EV mode and the HEV mode so that the battery's SOC is maintained within a normal range. That is, the hybrid system is controlled so that the EV region is reduced and the HEV region is extended when the battery's SOC is below a predetermined value and a driver's torque requisition is above a predetermined value. Conversely, the HEV region is reduced and the EV region is extended when the battery's SOC is above a second predetermined value and the driver's torque requisition is below another predetermined value.
FIG. 1 is a schematic diagram showing a conventional technique for controlling transition between an EV mode and an HEV mode in a hybrid vehicle, in which the transition between the EV mode and the HEV mode is controlled based on the following factors. First, an engine on map value for entering the HEV mode is determined based on the battery's SOC and the vehicle speed. Moreover, a hysteresis map value is determined based on the battery's SOC and the vehicle speed to prevent frequent transition between the EV mode and the HEV mode. Furthermore, the driver's torque requisition is calculated by monitoring the accelerator position sensor and the gear position sensor.
Then, it is determined whether the vehicle enters into the EV mode or the HEV mode based on the determined engine on map value and hysteresis map value and the calculated driver torque requisition. That is, when the driver's torque requisition is greater than the engine on map value and exceeds the hysteresis map value, the vehicle enters into the HEV mode and, when the driver's request torque is smaller than the engine on map value and exceeds the hysteresis map value, the vehicle enters into the EV mode.
However, when the engine on map value and the hysteresis map value are determined based on only by the battery's SOC and the vehicle speed in the conventional control technique, the on/off control of the engine and the control of power distribution between the engine and the motor may be inefficient. In other words, the conventional control technique does not reflect other variables that may affect the on/off control of the engine and the control of power distribution between the engine and the motor, thereby having a negative impact on the fuel efficiency and driving performance of the hybrid vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.